1. Field of the Invention
The present invention relates to signal processing apparatuses, signal processing methods, and programs, and particularly relates to a signal processing apparatus capable of more easily and more reliably detecting noise, a signal processing method, and a program.
2. Description of the Related Art
In apparatuses which collect sound using incorporated microphones such as IC recorders, for example, it is likely that noise referred to as “touch noise” is generated since users touch the apparatuses when sound is collected.
In particular, click noise is generated due to energy integrated within a short period of time when various functional switches are clicked during recording and is output as abnormal noise which is not masked by other sounds at a time of reproduction of the collected sound and which is offensive to the ear. Therefore, there is a demand for a technique of detecting and reducing such click noise.
As a method for reducing click noise, a method for performing filter processing on a signal to be processed using a high-pass filter and detecting click noise using a ratio of a maximum value to a movement average value (refer to Japanese Examined Patent Application Publication No. 7-105692, for example) and a method for detecting click noise using a difference between a maximum value and a minimum value in a frame (refer to Japanese Patent No. 3420831, for example) have been proposed.
However, in these methods, if the signal to be processed includes a portion corresponding to high energy and a portion corresponding to low energy, not only click noise but also music, voice (especially, consonant), and the like may be detected as click noise. For example, a signal having high energy level for a certain period may be detected as the click noise.
Therefore, a method for detecting a persistence length of a pulse signal and determining that the signal is not click noise but a music signal when the persistence length is equal to or larger than a certain length has been proposed (refer to Japanese Patent No. 2702446, for example).